Getting a blank page when clicking on products - HELP!

I am using Zen Cart 1.3.8. on OS X 10.5.
My site: https://www.tamo.no -has been working perfectly until now. The only thing I have changed is overwriting includes/classes/order.php in order to make sure the stock by attributes works properly.

Can anyone help me? - URGENTLY!

Since that mod modifies tpl_product_info_display.php, I'd check that file first and upload a fresh copy if necessary.

I have now replaced

includes/templates/template_default/templates/tpl_product_info_display.php

with the original file, but it didn't help.

If you installed the Stock by attributes mod properly, there should be a copy of that file in templates/YOURCUSTOMTEMPLATE/templates that is controlling things.

OK, what I have done so far is the following:

Yesterday, in order to fix the problem with Stock by Attributes (it did not update the stock), I followed the instructions given by limelites here:

http://www.zen-cart.com/forum/showthread.php?t=34977&page=65

I downloaded the "stock_by_attributes_4-7MULTIADD mod" since the version I'm using (4.7ajax) does not include the file "/includes/classes/order.php".

I replaced my /includes/classes/order.php with the file in the 4-7MULTIADD mod.

Since then, my products are not showing. I have tried to revert the situation by replacing order.php with the original zen cart file.

I have also replaced tpl_product_info_display.php both in includes/templates/template_default/templates/ and templates/YOURCUSTOMTEMPLATE/templates - but to no avail.

Can the admin log have something to do with this?

Sorry, but I could really use some help on this one...